This invention relates to a counterbalance device for a manipulator of, for instance, a laser knife in which the moment of the knife within the permissible range of movement thereof is maintained in a balanced state so that the operability of the device is remarkably improved.
The manipulator of a laser knife is a device in which several hollow light conducting paths of different lengths are coupled to one another by means of mirrors to form a single flexible light conducting path for introducing and focusing laser beams emitted by a laser oscillator onto a desired position.
Typically, the weight of such a manipulator is several kilograms. The dynamical fulcrum which is provided for supporting the manipulator is positioned in the vicinity of the input end of the laser beams. The position of the center of gravity of the manipulator is irregularly shifted as the manipulator is operated and, accordingly, the moment of the manipulator with respect to the dynamical fulcrum is also irregularly changed. To compensate for this, a counterbalance device may be provided the prime purpose of which is to provide selected weight on the side opposite, with respect to the dynamical fulcrum, to the manipulator to support the latter and to thereby eliminate moment unbalance due to movement of the center of gravity of the manipulator.
A conventional counterbalance device for a laser knife is so designed that, as described in the specification of U.S. Pat. No. 3,913,582, the moment is maintained in a balanced state only when the manipulator rests at a single predetermined position. Such a conventional counterbalance device is disadvantageous in the following points. First, it cannot eliminate moment unbalance due to movement of the center of gravity of the manipulator. Secondly, the moment is increased or decreased in proportion to the amount of shift of the center of gravity of the manipulator from its initial position. This unbalance of moment produces a high resistance to manual movement by the operator when he is operating the manipulator. This is a serious disadvantage in a surgical operation as it may distract the operator from concentrating his attention on the delicate techniques usually involved in such procedures.
Accordingly, a first object of the invention is to eliminate moment unbalance caused by movement of the center of gravity of a manipulator as the latter is operated by continuously controlling a counterbalance system in association with the operation of the manipulator.
A second object of the invention is to improve the operability of the manipulator for both fine and coarse operational modes by eliminating moment unbalanced states.
A third object of the invention is to maintain the moment balance of the manipulator stable at all times thereby to protect its multi-articulation mirror coupling mechanism from excessive force and to maintain the required extremely high stability of the laser beam light conducting system and its optical axis.